api.js

import axios from 'axios';
import MockAdapter from 'axios-mock-adapter';

const api = axios.create({
  baseURL: '...',
});

export const mock = new MockAdapter(api, { delayResponse: 2000 });

export default api;

users.js

import api, { mock } from './api';

mock.onGet('/users').reply(200, require('./users.json').fetch);

const fetch = async () => {
  const response = await api.get('/users');

  return response.data;
};

export default {
  fetch,
};

users.json

{
  "fetch": [
    // ...users
  ]
}